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What causes this fireside residue?

D107 Member Posts: 1,852
4 year old Buderus G115/3, Riello 40 F3, .50 60W nozzle. Every annual tuneup there's about a good quart of powder in the chamber and baffle area. Tech came today for an unrelated minor adjustment and when i mentioned this he said it comes from not burning right. Now that we have this nozzle and pump pressure at 160 it's been running like a charm, quiet, no more impingement like we used to have with the 80 nozzles, etc. all the draft and CO2 numbers are good.

Stack temp always 325 to 350 gross. Chimney lined with stainless steel. Always get a sprinkling yellowish dust out of breech pipe on floor which I figure is condensation. I understand Firedragon's opinion is that stack temp should be 400F.

I can see how condensation(if that's the culprit) might cause the yellow/red dust in the breeching, but that wouldn't cause the reddish dust in the photo all the way in the fireside would it? happy to remove or adjust the baffles to raise temp if necessary.

I'd be surprised if the cause was improper combustion, but i've heard here and elsewhere that the boiler fireside should basically be clean upon annual inspection. It's not a big deal for the company to vac it out once a year, but figure it's better if it could run without the residue.


  • Glen Aspen_2
    Glen Aspen_2 Member Posts: 53
    have you considered -

    that it is a combination of a slightly low stack temp (like firedragon I would think your figures should be NETT not gross) & return water temps are on the low side. You didn't state operating conditions - so I can only speculate.
  • Robert_25
    Robert_25 Member Posts: 530
    edited September 2010
    Dye used in Fuel

    I believe the red colored power is actually ash from the red dye used in the fuel.  I have the same thing in my boiler, which is kept "at-temp" and has a gross stack temperature of about 450F.

  • D107
    D107 Member Posts: 1,852
    Thanks for feedback

    I didn't mention that boiler is on outdoor reset with Logomatic. It's interesting that in 2008 Buderus revised its stack temp requirements for this boiler to say: "Appoximate gross stack temp: 289degrees" for chimney vents.

    Mine has an insulated liner which would be optimum but 289 seems too low. Originally it did say 350 gross, which itself was probably too low. The listed required liner diameter for this boiler is 5 inches and I'm wondering would a 4 inch liner keep the temps higher and still vent properly? it's an 18ft external chimney above the breech. Total equivalent piping length of breeching is 16.5 ft (at best should be 13.5 but that's not too bad.) Also there is no FAI but house is fairly loose mid-50s split level.

  • R Mannino
    R Mannino Member Posts: 440
    With A Buderus

    That's pretty much what you get. They run a little cleaner with an NX.
  • D107
    D107 Member Posts: 1,852
    Possible Solution: Raise Pump Logic Setting

    Thanks for the photo Rick. Here's a possible solution to this problem and some I think valuable Buderus info from a very knowledgeable tech:

    "I would agree that it is probably a mixture of the fuel dye and a little condensation

    based on the information I read (yellow dust). The fuel dye is not normally an

    issue and not much that can be done about it. If there is other residue, that

    has a slight odor of sulfur or “eggs”, then it is flue gas condensation mixed

    with the sulfur from the fuel. If there is a good amount of this type of

    residue, the best way to clean this sulfur is with water. After the boiler is

    completely vacuumed, if it’s sprayed with a little water from a spray bottle,

    it just melts away (very messy job!  Most technicians do not do – can’t

    blame them). I have only done it to my G115 boiler once or twice in thirteen


    (Note: The sulfur content can vary dramatically between oil deliveries. A colleague

    orders oil from the same company I do and when we tested the oil in our tanks,

    there was a 100ppm difference. He is on automatic delivery, receiving oil

    approximately once a month during the winter, where I normally only get a

    couple deliveries a year.)

    If the burner is set up correctly, check the “pump logic” on the R2107 (Can be

    found in the Service level of the R2107 programming). If at the factory setting

    of 104, I would increase it to 115. If the R2107 is wired properly, the “Pump

    logic” will prevent the circulators from operating, only when the burner is

    running. When the call for the burner to light is initiated, the R2107

    “pump logic” will allow the circulators to operate if the boiler is above the

    “Pump logic” setting.  When the boiler is at this higher temperature there

    is less chance of the return water causing flue gas condensation in the boiler.

    Most technicians don’t understand how the “pump logic” works and why it’s so

    important to wire the circulators into the R2107 control. If the burner is not

    running, the “pump logic” does not affect the heating curve, programming or

    other functions of the R2107. 

    I raised my pump logic setting to 115 after the first couple of years of

    installing the G115 and since have had very little condensate residue.

    About 2 years ago I installed the GB125BE boiler (oil fired condensing

    boiler – basically the G115 with a Buderus oil burner and a heat exchanger

    mounted on the rear of the boiler for the return water) as a test site and set the

    pump logic at 115 from the start. I have both boilers installed and

    operational in my house, but use the GB125BE exclusively. I have very little if any

    condensate issues in either boiler. I fire the G115 about every other month just to

    keep it on standby. 

    (The “pump logic” normally does not affect the domestic hot water production, as

    the R2107 does not allow the circulator for the domestic hot water to operate

    until the boiler temperature is above the tank temperature. This prevents the

    domestic hot water loop from heating the boiler. In a standard control system

    with domestic hot water, if there is a call for heat and the boiler is cold,

    the cold boiler water is circulated through the indirect loop and “robs” heat

    from the domestic hot water tank. This can reduce the domestic hot water output

    of a tank. The R2107 domestic hot water differential is approximately 7

    degrees, which normally allows adequate time for the boiler to achieve the pump

    logic setting temperature before there is an effect of domestic hot water

    output. The R2107 domestic hot water production feature is quite unique. It

    actually “learns” the domestic hot water load over time and adjusts what the

    boiler temperature needed is to satisfy the demand.  It can differentiate

    between a stand by temperature loss or domestic hot water usage. In the case of

    a stand by loss, the R2107 will fire the boiler temperature about 25 degrees

    higher than the DHW setting, then circulate the boiler water till the tank

    reaches temperature.) 

    (Note: A Taco relay will not light up during domestic water production. Normally

    if the domestic hot water circuit is wired to the Taco relay there are issues

    with domestic hot water production. Such as during the R2107’s “Summer” mode

    the circulators wired into the Taco relay board are not operation, so there

    would be no domestic hot water during the summer time.)

    The smaller nozzle, higher pump pressure is a direction that is becoming more

    and more acceptable here in the United States. You are correct, about three

    years ago, Buderus did its own certified testing and found the smaller nozzle

    and high pump pressure did provide better combustion, less impingement issues

    and cleaner combustion chambers. This theory has been used in Europe for years.

    Most technicians have a preference of oil burners, mostly depended on which one

    they know best, but the Riello burner still outsells the other two

    manufactures combined.

    I checked the stack temperatures that I have and on the G115/28 with the

    Beckett NX = 410 degrees, baffles are pulled. The GB125BE22 stack temperature

    has been as low as 140 degrees during a heat cycle and 180 degrees during a

    typical domestic hot water production cycle (both of the boilers in my home are

    direct vents). In my opinion a gross stack temperature of 289 is low for

    an outside chimney. In my opinion I would look for around approximately a 350

    degree, gross stack temperature with the Riello burner.

    I agree trying the pump logic adjustment first, and then proceeding with

    turning or pulling the baffles if not resolved."
  • Jack
    Jack Member Posts: 1,047
    Check appendix E in NFPA 31

    It being an Appendix it is not a part of the code, but you can use it as a guideline for some sizing issues. I don't have my copy handy, so cannot say for sure on the 4" change, but if you want to try it, I'd suggest using 4" pellet vent.it is Type L rated and insulated, which will give you the best chance of success in this configuration.

    I have said before that when Rich Krajewski from Brookhaven put these tables out I spoke with him about them and he said that the single greatest impact on successful drfat in operation in all of his models was an insulated vent connector.

    That will make pellet vent work on 4" and for 6" you could use the DS and DVL close clearance vent connector pipe fron Selkirk and DuraVent respectively. Hearthe supply is the best place to source these materials. 5" all fuel is available but check the listings. If it is tested to 103 ht it can only be used a max of 30 deg from vertical. I've been away from that business for a while but think these things have not changed.
  • D107
    D107 Member Posts: 1,852
    edited September 2010
    vent size

    Thanks for your comment Jack. On changing the vent size I was advised:

    "...I would not suggest reducing the vent size, especially with the height and distance between the boiler and chimney. A small vent size may cause other issues and may require manufacturer’s approval to meet code."

    Note that the current 5" liner is insulated, but admittedly there was only room in the chimney for less than an inch of insulation all around. But I'll check out the info in your post. Thanks.
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